The present invention relates to burner nozzle tips adapted for use on pulverized coal-fired furnaces and, more particularly, to tilting nozzle tips for burners on pulverized coal-fired furnaces utilizing tangential firing.
One common method of firing coal in conventional coal-fired steam generating boiler furnaces is known as tangential firing. In this method pulverized coal is introduced into the furnace in a primary air stream through burners, frequently termed fuel-air admission assemblies, located in the corner windboxes of the furnace. The pulverized coal-air streams discharging from these burners are aimed tangentially to an imaginary circle in the middle of the furnace to create a massive flame therein termed a fireball.
Upon leaving the furnace proper, the combustion products formed in the fireball pass through a boiler section typically housing a superheater, a reheater, and other various heat absorption surface to cool the combustion products and generate superheated steam. By changing the position of the fireball formed in the furnace upon convergence of the fuel-air streams emanating from the burners, control of the temperature of the steam leaving the superheater or reheater is achieved. By tilting the burner nozzle tips in unison the fireball can be physically raised or lowered within the furnace so as to increase or decrease the heat absorption by the furnace waterwalls thereby raising or lowering the temperature of the combustion products leaving the furnace proper to pass over the superheater and reheater surface. As the temperature of the combustion products entering the boiler section changes, the temperature of the steam generated in the heat absorption surface disposed therein changes proportionally. Such as method of steam temperature control is shown in U.S. Pat. No. 2,363,875 to Kreisinger et al, issued Nov. 28, 1944.
A typical coal-air admission assembly or burner employed heretofore on a tangentially-fired furnace comprises a coal delivery pipe, often termed a coal nozzle, through which pulverized coal entrained in a primary air stream is delivered to the furnace, an air conduit surrounding the coal delivery pipe through which additional air is delivered to the furnace, and a nozzle tip pivotally mounted to the coal delivery pipe so as to be tiltable in a vertical plane whereby the pulverized coal-air stream being delivered to the furnace through the coal delivery pipe and the additional air passing through the air conduit can be directly discharged into the furnace as dictated by steam temperature requirements.
A typical prior art burner nozzle tip, such as that shown in U.S. Pat. No. 2,895,435 to Bogot et al, issued July 21, 1959, was formed of a steel open-ended inner shell defining a flow passageway through which the pulverized coal-air stream from the coal delivery pipe is delivered into the furnace and a steel open-ended outer shell spaced from and surrounding the inner shell so as to define an annular duct through which the air leaving the air conduit is directed into the furnace. Additionally, one or more steel or stainless steel baffles, termed splitter plates, are typically disposed within the inner shell of the nozzle tip and aligned parallel to the longitudinal axis thereof, to impart additional directional force to the coal-air stream discharging through the inner shell and to ensure a uniform distribution of the coal-air stream particularly when the nozzle tip is tilted away from the horizontal.
A major problem heretofore encountered in using such nozzle tips has been the rapid wear of the steel or stainless steel splitter plates due to extreme erosion caused by the impingement of coal particles entrained in the high velocity air stream passing from the coal delivery pipe. As these splitter plates wear away, they lose their ability to adequately direct the pulverized coal-air stream into the furnace, thus detracting from the effectiveness of the nozzle tip in controlling steam temperature.
More importantly, as the splitter plates wear away, more and more coal particles bypass the plates and impinge upon the walls of the inner shell when the nozzle tips are tilted away from the horizontal resulting in increased and more rapid wear of the shell itself. Consequently, these prior art nozzle tips must be replaced more often than preferred and more frequently than would be necessary if the inner shell of the nozzle tips had not been exposed to the erosive effect of the impinging coal particles.